There is an increasing need for security markings that are unique and difficult to counterfeit, compatible with existing machine reading systems, and low in cost. Particularly, there is a need for nearly invisible and colorless security markings that still are readable in the visible region with conventional visible machine readers, such as a visible bar code scanner, and that can be read on transparent backings or substrates, such as found in clear packaging materials.
There are nearly invisible and colorless security markings that have infrared absorption, are imageable with infrared lasers, and are readable in the infrared region with conventional infrared machine readers, such as an infrared bar code scanner or camera, as for example described in U.S. Pat. Nos. 6,381,059 and 6,589,451, both to Carlson. However, these security markings on a transparent backing or substrate, as in a clear packaging or in a clear card, are not readable in the visible region with existing visible bar code scanners and other visible readers.
It would be advantageous if a laser imageable media were available for use in a variety of nearly invisible and colorless security markings on transparent substrates that are easy to read with conventional visible bar code scanners. It would be particularly advantageous if this laser imageable media had the flexibility to also form an infrared image that is easy to read with conventional infrared bar code scanners.